Provision of signage, specifically advertisements on large areas, such as building facades, is a common business for a long time. Most of the display devices that are designed for those purposes are nowadays electronically controllable to be easily updatable. This is particularly important when information to be provided is related to the road direction or other massages and other advertisements.
The electronically controlled optical displays are based on two types of display techniques referred to as “passive” wherein one external light source is required to change an optical property of the display device, and as “active” that ensures an optical display device to be self-luminous.
Known examples of active optical displays are matrix arrays of light-emitting diodes (LEDs) that comprise discrete dots (so-called “pixels) being individually electronically controlled in their brightness and colors.
One known example of an active optical display system is that described in the patent document EA004517 (B1), which comprises light-emitting elements; electrodes; contact pads and light-emitting element control unit; at least one glass-packet with light-emitting elements inside; wherein the control unit consists of the inward glass-packet light-emitting element control part, placed inside that glass-packet, and the part to control the information display system in general, based outside the glass-packet. The information display system characterized in that the glass-packet at the same time is a part of building glazing and/or is architecture or construction element; light-emitting diodes, incandescent lamps and/or other light emitters are used for light-emitting elements; it has plain, bent and/or tubular shape; the glass-packet surface is covered with clarifying, lightsharing, heatreflecting and/or solarblocking coating; the light-emitting elements inside the glass-packet are fixed to the glass directly, or with lattice, strings, rods or similar construction elements, which provide regular arrangement; light-emitting elements, for instance light-emitting diodes, are placed in a way to provide two way directional information flow without transparent surfaces functionality failures; and it is operated in static and/or dynamic mode of displaying.
Such active optical display devices are not transparent when they are in off state and therefore they block the light passage completely, or at least partially.
The optical display devices having such features are limited in their application range particularly in building facades including windows, since they can deteriorate the normal function of a window by worsening the daylight intake as well as view through the window at night.
In an attempt to eliminate the above mentioned drawback of self-luminous display devises many different solutions have been proposed, such as for example disclosed in German patent application DE 2002220828 (2002 October), which comprises at least one optically transparent layer and light emitting elements with respective leads for individually controlling the elements. To ensure the see-through capabilities of a windowpane the leads are made as small as possible—not greater than 0.1 mm, especially not greater than 0.05 mm.
However, when the display is switched on at night, the information through it can be visible not only outside of a building but to the people inside the room where the display is used as a windowpane. This is not always desirable, particularly in office rooms wherein the people are performing their daily tasks and the information displayed through room windows, particularly the dynamically changing images, may disrupt the office workers normal operation.
Even at daytime, when the display is turned off the windowpane still remains not completely transparent since number of such leads is very high and the thin lines of opaque leads are still visible that may not be desirable in aesthetic point of view.
The above example shows that it would be desirable to have high transparency and one-way through vision capability so that an active display could have extensive application.
In order to enhance the transparency of the active display devices, a certain type of light emitting elements, so called OLEDs, i.e. Organic Light Emitting Diods, such as described in U.S. Pat. No. 6,345,328, are used nowadays. The thin organic layers contained in OLEDs are particularly transparent in off state.
However OLED material, i.e. a thin organic layer, appears colored to the human eye when it is off state.